1. Field of the Invention
The present invention relates to a wheelchair lift system facilitating transit between different horizontal levels for persons otherwise unable to make the transit unassisted. A particular embodiment of this invention is coupled to stairways and is used to accommodate persons incapable of traversing stairs unassisted. More particularly, this invention allows for a safe transit up or down a stairway for those persons who are capable of traveling about on a level floor yet have difficulty negotiating stairs, such persons including but not limited to, cardiac patients, "walker" patients, and patients in wheelchairs. Yet more particularly, this invention relates to a novel system allowing for the smooth transit between horizontal elevations using a rolling platform in conjunction with tracks which are varied in elevation by means of a motor coupled to the tracks without using cables, a motor that can be activated by a wheelchair occupant or other user without any assistance. Most particularly, the preferred embodiment of the present invention uses worm-gears arrayed in such a way as to allow for a safe return to the lower level in the event of a power failure. Finally, the wheelchair lift system of the present invention, when installed on a stairway as to the preferred embodiment, does not prevent that stairway from being traversed in its normal manner.
2. Description of the Prior Art
Motorized lift systems for stairways have been around for a long time, serving to transport persons incapable of otherwise negotiating stairs. Most such systems had to be custom-made for particular locations and stairs. For instance, the most common lift system for transporting persons up a set of stairs used a fixed rail which in turn was attached to a stairway wall somewhat like a very strong bannister. The fixed rail was custom-manufactured to fit the entire run of stairs upon which it would be used. A lifting chair was attached to the rail and the chair moved between levels using a motorized cabling system or using a direct-drive motor attached to the chair itself. For a wheelchair-bound person, this system required, generally, that the person be physically transferred out of a wheelchair and into the movable chair, and then, after the person traversed the stairs, that he or she be removed from the lift chair and placed into either a second wheelchair or into the first wheelchair which would have been carried by an attendant the length of the stairway.
More recent lift systems have been devised that are portable, self-contained devices adaptable to almost any stairs encountered. U.S. Pat. No. 3,229,788 (1966, Booth) teaches such a system. Booth provides a wheelchair-supporting platform riding on wheels engaged in a track and controlled by a motorized cabling system. For motive force, Booth uses two reversible electric motors. Each motor is connected to a reduction gear box coupled to the axle of a drum onto which is affixed one end of a cable. This cable is then threaded around a series of pulleys, including those rotatably mounted to a wheel axle of the platform, and secured to the upper end of the track on which the wheels rest. In order to lift the platform along the track, the drum is rotated so as to draw the cable shorter. The entire system of motors, gear box, and pulleys is secured to the lifting platform.
Another system, more closely antecedent to the present invention, is that of U.S. Pat. No. 4,674,601 (1987, Benjamin). Benjamin describes an apparatus for enabling wheelchair-confined individuals to more easily convey themselves between two different elevations, especially between the inside ground level of a house and the outside ground level. The key to Benjamin is a unitary molded arcuate lift or scoop on which the wheelchair rides while being conveyed between the two levels. As the scoop rotates up, the wheelchair rolls forward and eventually onto the upper level. The scoop is mounted in a frame in which also resides the peripheral equipment needed to effect the scoop's raising and lowering. The lower end of the scoop in Benjamin is attached to a pair of cables which pass up to and through the top of the frame and then around take-up reels. The opposite end of the scoop is attached by a hinge to the frame at the level of the higher elevation.
Problems associated with the earlier systems include expense and lead-time requirements inherent in custom-made apparatus, complexity of the portable cable-based devices, and, in the case of the arcuate system of Benjamin, the need to keep the wheelchair unlocked during use. Even though the portable system of Booth does not require the excessive lead time and high monetary outlay of the custom-made systems, it has other significant problems. For example, the large number of pulleys required for motor-torque reasons in systems such as that of Booth increases the likelihood of component failure and consequent down-time. Furthermore, where, as in Booth, all of the components are secured to the platform, any repair to the motor, cable, or pulleys requires the disassembly of the platform for access. Although one of the touted advantages of Booth is its portability, nevertheless, from a practical viewpoint, the weight of two synchronized motors, two reduction gear boxes, multiple pulleys, cables, tracks, support members, and platform make the system somewhat burdensome to transport, to say the least.
The molded, arcuate lift system of Benjamin suffers a major regulatory disadvantage. For it to work properly, the wheelchair must be free-rolling; that is, the wheelchair wheels must not be locked. Although this system should be quite safe, it confronts a regulatory barrier in the widespread requirement that wheelchair wheels be locked during transit of the wheelchair between different levels.
Therefore, what is needed is a wheelchair lift system combining the sturdiness of a fixed system, the minimal manufacturing lead time of a portable system, and the simplicity of an arcuate molded platform lift system, while readily complying with the existing regulatory framework. What is further needed is such a system that can be installed in a stairway without precluding normal access to that stairway. What is yet further needed is such a lift system that utilizes only a small number of components and that utilizes standardized components, so as to minimize breakdown frequency and also the attendant down-time when breakdown does occur.